Sara wanted to perform a scientific experiment relating to the effect of ultraviolet (UV) light on the survival rate of microscopic protists in pond water. She went to a local pond and collected a large bucket of pond
water, then poured 500 milliliters of the pond water into each of two identical glass jars.
She viewed a small sample of the pond water under a compound light microscope to verify that the water
contained multiple species of microscopic protozoa. She was also able to get a rough count of the
organisms in her sample using a special microscope slide. To set up her experiment Sara took one of the
glass jars with pond water and protists, labelled it "100, and placed it 10 centimeters under a lamp that
transmits 100% UV light. The other jar, she labelled "0" and placed it 10 centimeters under a lamp that
transmits 0% UV light. After the pond water/protist mixture in both jars was exposed to the lights for 8
hours, she collected samples from both jars. She used the same procedure as before and made a 2nd
count of the microorganisms to compare her first count.
What is the independent variable.